Abstract:
To apply accurate procedures of structural analysis
that are now available, the behavior of nailed joints in
light-frame wood buildings under long-term loads needs to
be studied. Such a behavior can best be evaluated by
testing specimens under constant loads, which requires
relatively simple testing arrangements. To provide for a
practical use of the constant-load test results,
theoretical models were developed that predict the
behavior of nailed joints under varying loads that are
subjected to wood structures in service.
Existing models and principles were used to develop
five new general models, all of which account for the
nonlinear viscous-viscoelastic behavior of nailed joints.
The models incorporated the modified superposition
principle and strain hardening principle. Heaviside
function and Fourier series were also incorporated to
describe varying loads that can be either discrete or
mathematically defined continuous function.
To develop experimental data needed for the
formulation and verification of the models developed, joints made of Douglas-fir lumber, plywood and 6d nails
were tested under four constant and four varying loads.
The experimental data for constant loads were used to
formulate specific theoretical models which were further
modified for varying loads. The comparison between the
predicted and the corresponding test results shows a very
good agreement for all the specific models. The models
that include the modified superposition principle are the
most accurate and the simplest to apply to nailed joints
under discrete load functions. Fourier series
representation of varying-load functions shows a great
potential for practical applications, because it can
represent the service loads more accurately than the
discrete approximation.
The specific models presented are limited to the type
of joints used in this investigation. Other types of
joints need to be tested under constant loads to develop
appropriate equations that describe their creep behavior
under varying loads.
